In a span of four months, the father of U.S. Rep. Patrick Murphy, D-Jupiter, and his business interests poured a half-million dollars into a super PAC supporting his son's bid for U.S. Senate.

In mid-December, Thomas Murphygave $200,000 of his own money to "Floridians for a Strong Middle Class," and then on March 31, Thomas Murphy's Miami-based construction company -- Coastal Construction Group -- shelled out $300,000 to the super PAC.

The $300,000 donation was revealed Friday when the super PAC's quarterly financial disclosure was made available online through the Federal Election Commission. It accounted for 74 percent of the super PAC's intake between January and March, the report showed.

In all, "Floridians for a Strong Middle Class" reported $405,000 in contributions for the first quarter, entering April with $841,300 in cash on hand.

Since the super PAC was established about a year ago, 29 people or companies have donated $965,000 to it. The two donations from Murphy's father and his company account for 52 percent of that total income.

The funds are separate from Murphy's individual campaign account, which on Monday reported raising about $2 million in the first quarter and having $5.6 million in cash on hand.

The Poarch Band of Creek Indians in Alabama has emerged as another top donor for "Floridians for a Strong Middle Class." The tribe gave another $50,000 in March, after first giving $50,000 last year.

Super PACs are not bound by the $2,700-per-race cap on individual contributions, as candidate's campaign committees are, nor can they coordinate directly with the candidate.

Patrick Murphy has been critical of the growing prominence and plethora of super PACs in the modern political era, despite benefiting from them both in this election and in his first U.S. House race.

Murphy's Senate campaign declined to comment today on his father's company's donation to the super PAC last quarter, and a representative of "Floridians for a Strong Middle Class" would not comment directly on it either.

"Patrick Murphy is a proven leader who has stood up for Florida's hard-working families, and as our next Senator he will continue to invest in ways to grow and strengthen Florida's middle class. His record on standing up for Florida's families is exactly why our efforts are receiving broad support," Ashley Walker, the super PAC's senior adviser, said in a statement.

Thomas Murphy has a history of giving sizable donations to super PACs supporting his son. In Patrick Murphy's first U.S. House race in 2012, Thomas Murphy gave $250,000 to the pro-Murphy super PAC American Sunrise.

Murphy faces a contentious August primary against fellow U.S. Rep. Alan Grayson, D-Orlando, in a bid for Marco Rubio's U.S. Senate seat. Grayson does not appear to have a super PAC supporting him.

Among the five Republican candidates in the race, several have super PACs supporting them.